1. Field of the Invention
This invention relates generally to bathtubs and to the manufacture of bathtubs, and more particularly to a steel bathtub having a sloped end for use as a back-rest.
Modern bathtubs are typically made in three types of media, namely: cast iron, drawn steel, and molded plastic. Bathtubs are typically made in lengths of 4 ft., 41/2 ft. and 5 ft. The 5 ft. length is probably the most typical.
For those who like to sit and soak in a bathtub, it is desirable for the bathtub to have a sloped back end. The present process description refers to this as an "incline end" bathtub. The "incline end" bathtub typically has a slightly inclined bottom, and a front end wall and two side walls that are substantially vertical, while the back end wall is inclined at a gradual angle. This shape is easy to produce in plastic or cast iron. This shape is not easy to produce in a sheet steel drawing operation, however, because the nature of the draw at the back end is so different from the draw around the front and sides.
A principal problem encountered in forming such a steel bathtub with a sloped back end is that the back end material naturally tends to wrinkle as the steel sheet is drawn. The present invention is directed to solving this problem in the manufacture of "incline end" bathtubs.
2. Description of the Related Art
The closest prior art in the form of U.S. patents which has been discovered is as follows:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,438,111 Wilcox Apr. 15, 1969 3,496,896 Smith Feb. 24, 1970 3,543,559 Hawkins et al. Dec. 1, 1970 4,357,816 Antonov et al. Nov. 9, 1982 4,470,287 Antonov et al. Sep. 11, 1984 ______________________________________
The Smith U.S. Pat. No. 3,496,896 discloses a method of making a foil pan using a punch and die wherein the punch and die each have a cavity area. As the pan is formed from a blank, circumferentially spaced corrugations form in the side wall of the pan as a natural consequence of the drawing and stamping process. The cavities in the punch and die permit these corrugations to form without restriction.
In the Wilcox U.S. Pat. No. 3,438,111, a method of making a wheel rim from sheet stock comprises a series of drawing and stamping operations to produce a contoured article with varying wall thickness. In one step of the process, a circumferential recess is formed prior to ironing the blank into a radial flange.
A method described in the Hawkins U.S. Pat. No. 3,543,559 uses a specially formed die with spaced grooves to take advantage of the buckling of the sheet stock as it is drawn in the stamping process. The die grooves accommodate the buckled material to form corrugation ribs in the stamped article.
The Antonov U.S. Pat. No. 4,470,287 defines a method for producing hollow articles by deep drawing.
No prior art was discovered that described a process for drawing a bathtub from sheet steel where the bathtub has a sloped back end.